Paraffin hydroisomerization process

ABSTRACT

An improved hydro-isomerization catalyst composed of platinum and/or palladium distended as very small crystallites on a hydrogen form mordenite base is disclosed. The catalyst is prepared by distending the noble metal on the base by addition of small quantities of cerium nitrate in admixture with the noble metal followed by controlled calcination to achieve an almost monatomic dispersion of the noble metal on the base. The catalyst thus prepared is used to isomerize normal paraffins in the C4 to C7 range in the presence of hydrogen at elevated temperature and pressure.

Parthasarathy et al.

[ Nov. 4, 1975 PARAFFIN HYDROISOMERIZATION PROCESS Inventors: R. Parthasarathy, Silver Spring;

James Michael Maselli, Columbia, both of Md.

W. R. Grace & C0., New York, NY.

Filed: Aug. 9, 1973 Appl. N0.: 387,074

Assignee:

US. Cl. 260/683.65; 252/455 Z Int. Cl. C07C 5/30 Field of Search 260/683.65

References Cited UNITED STATES PATENTS 1/1967 Adams et a1 Zoo/683.65 2/1968 Plank et a1. 260/68165 Benesi 260/683.65

Hirschler 260/683l65 Primary Examiner--Paul M. Coughlan, Jr. Attorney, Agent, or Firm-Joseph P. Nigon [57] ABSTRACT An improved hydro-isomerization catalyst composed of platinum and/or palladium distended as very small crystallites on a hydrogen form mordenite base is disclosed. The catalyst is prepared by distending the noble metal on the base by addition of small quantities of cerium nitrate in admixture with the noble metal followed by controlled calcination to achieve an almost monatomic dispersion of the noble metal on the base. The catalyst thus prepared is used to isomerize normal paraffins in the C to C range in the presence of hydrogen at elevated temperature and pressure.

1 Claim, No Drawings PARAFFIN HYDROISOMERIZATION PROCESS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates catalytic isomerization of low molecular weight normal paraflins. More particularly, it relates to the method of preparing paraffin hydro-isomeri zation catalysts comprising platinum or a palladium metal highly dispersed and homogeneously distributed into and onto a synthetic crystalline aluminosilicate mordenite support.

2. Description of the Prior Art Isomerization of low molecular weight normal parraffins having 4-7 carbon atoms per molecule is a well established process in the petroleum refining industry. This catalytic isomerization requires an acidic catalyst. Earlier processes relied on strongly acidic Friedel- Crafts catalyst such as acid promoted aluminum chloride. Comercial refining processes favor the use of heterogeneous catalysts; however, and various isomerization processes have been developed that use acidacting refractory oxide catalysts. Recently noble metal catalysts based on a hydrogen form of a crystalline alumino silicate. Mordenite has been shown to be equally effective. Further improvement have been achieved by preferentially acid leveling the mordenite to increase the silica-alumina ratio before incorporation of the hydrogenation component.

The mordenite form of the zeolites particularly the synthetic mordenite form has been disclosed in U.S. Pat. No. 3,190,939, to Benesi, issued June 1965 and U.S. Pat. No. 3,299,153, to Adams, issued January 1967. One of the problems that must be solved in isomerization catalysts is the prevention of excessive hydrocracking. The addition of noble metals to the mordenite catalyst base tends to reduce cracking. However, the catalyst previously proposed, even those containing noble metals, still require improvement in the reduc-' tion of cracking. It is particularly important to improve the selectivity to branched isomers and to increase process stability.

The incentive for an efficient process for isomerization of normal paraffins is apparent from a comparison of the octane numbers of normal pentane and normal hexane with their respective isomers.

Research Compound Octane Number n-Pentane 61.7 Isopentane 92.3 n-Hexane 34 Z-Methylpentane 73.4 3-Meth ylpentane 74.5 2,2-Dimethylbutane 91.8 2,3-Dimethylbutane 103.5

BRIEF DESCRIPTION OF THE INVENTION We have developed a hydro-isomerization catalyst that is highly selective for preparation of isomers of the C to C normal paraffins and that effectively suppresses the percentage of the feedstock that undergoes hydrocracking. The catalyst is prepared by distending platinum and/or palladium on a hydrogen form mordenite support as very small crystallites. The distension onto and into the hydrogen form mordenite base is effected by incorporating the noble metals on the support in conjunction with small quantities (less than 5% by weight) of a soluble cerium salt followed by controlled calcination. This process achieves an almost monatomic dispersion of the noble metal on the hydrogen form mordenite base and results in a highly active and selective catalyst.

DETAILED DESCRIPTION OF THE INVENTION The first step in the process of our invention is the preparation of the catalyst base. The catalyst base is a commercially available mordenite. While mordenite is a naturally occurring mineral, a synthetic mordenite is available commercially from the Norton Company and marketed under the trade name Zeolon. Mordenite is characterized by its high silicon to aluminum ratio of about 5:1 and its crystal structure. It has a pore size of about 7 angstroms.

Conversion of the sodium form to the hydrogen form is achieved either by a direct replacement of sodium ions with hydrogen ions or by replacement of sodium ions with ammonium ions followed by decomposition of the ammonium form by calcination. At least 95, preferably about 99% of the alkali metal is removed by ion exchange.

The mordenite base can also be further improved by subjecting it to a sequential treatment with hot acid at a temperature of about 93 to 149C followed by treatment with cold acid at a temperature of lO-38C and by treatment with an ammonium compound.

For the acid treatment both organic and inorganic acids can be used. The strong acids are preferred. Examples of acids particularly suitable are the strong mineral acids such as phosphoric, sulfuric, nitric, and hydrochloric acids. Hydrochloric acid is especially suitable and is the preferred acid in both the hot and cold treating steps.

Usually aqueous solutions of the acid are preferred. The concentration may vary over a broad range of about 0.1 to 10 N. It is convenient and especially preferred to use an acid in aqueous solution of 2 N concentration. The hot'acid treating step is preferably carried out at about the boiling temperature of the acid solution. The cold acid treatment is conducted at a temperature in the range of 10 to 38C and preferably an ambient temperature.

The ammonium compound treating step is carried out with any ammonium compound which can form ammonium ions. However, aqueous solutions of neutral ammonium compounds are preferred, especially inorganic ammonium compounds such as ammonium hydroxide, ammonium chloride, ammonium sulfates, ammonium phosphates and ammonium nitrate. Ammonium nitrate is preferred. The concentration of the ammonium compound is not critical and can vary, for instance, from 0.1 to 5 M. However, it is preferred to use a solution of about 1 M concentration. The treatment of the ammonium compound can vary over a wide 3 ,9 l 7 ,7 39 3 4 range. It is preferred, that the treatment be carried out of such normal paraffms or hydrocarbon fractions rich at a temperature in the range of 93 to 149C at about in such normal paraffins. Suitable hydrocarbon fracthe boiling temperature. tions are the C to C straight-run fractions.

The essential feature of the process in the instant aplsomerization is conducted at temperatures in the plication is the method of distending the noble metals range of 400 to 650F and preferably about 500 to on the base. At isomerization temperatures noble metal 600F. At lower temperatures, conversion of normal catalysts lose activity with use. This, of course, requires paraffms is generally too low to be practical, although frequent catalyst replacements which are inconvenient, selectivity to isoparaffins is substantially 100%. At time consuming and costly. One of the reasons for the higher temperatures, conversion of normal paraffins is loss of activity of these noble metals is the surface miquite high; however, excessive cracking is encountered gration of the noble metal at elevated temperatures and selectivity to isoparaffins is low as a result. The which results in coalescing the small particles of the isomerization can be conducted over a wide range of noble metal crystallites into large crystallites. This crys-' space velocities, but in general the space velocity tallite growth in turn results in appreciable loss of speshould be in the range of about 0.5 to 10 and preferably cific surface area and hence catalytic activity. In our l to 5. Space velocity, as the term used herein, refers to novel process we disperse the noble metal crystallites in weight hourly space velocity and is expressed as weight the catalyst as crystallites in the 5 to 30 Angstrom size of feed per hour per unit weight of catalystflhe isomrange. This is indeed a very high degree of dispersion erization is carried out in the presence of hydrogen at a considering that the atomic diameters in noble metals pressure of 100 to 600 p.s.i.g., preferably 300 to 500 fall in the range of 2.7 to 2.9 angstrom units. p.s.i.g. and a hydrogen to hydrocarbon mole ratio of 3 The key to this unusual degree of dispersion of the to l to 10 to 1. catalyst in the instant invention is the use of low quanti- Our invention is illustrated by the following specific ties, generally less than 5% by weight, of soluble cerium but nonlimiting examples. salts in admixture with soluble salts of the noble metals in the impregnation step. The impregnation is followed EXAMPLE 1 by controlled calcination to achieve this very fine dis- This examples illustrates one suitable method of prepersion of noble metal on the catalyst. paring our hydroisomerization catalyst.

The noble metal, preferably palladium or platinum, Commercially available mordenite in the hydrogen can be incorporated from a solution of any soluble salt form was extruded as 1/16 inch extrudates. A 100 g. of the metal. Examples of suitable salts include the niportion of these extrudates was impregnated with a trate, ,the chloride, the tetraamine nitrate, etc. The nimixed solution of palladium nitrate (PdNO and cetrate is preferred. The impregnation or exchange is norrium nitrate Ce(NO .6H O. A sufficient quantity of mally carried out with a mixture of the noble metal salt the mixed salts was used to prepare a catalyst containand the cerium salt to give a noble metal content of ing 0.5% weight palladium and 1% weight C602. The about 0.02 weight percent basis finished catalyst and catalyst was calcined for 6 hours at 1000F prior to not exceeding abbut 5% by weight. It is preferred the charging to the reactor.

metal content be at least about 0.1% by weight and not over about 1.5% by weight. The cerium is present as EXAMPLE 2 about 0.1 to 5% by weight cerium oxide and preferably This example demonstrates the improvement 0.5 to 2% by weight. achieved by the dispersion of the palladium as a very This homogeneous distribution of the dispersed platifine dispersion on the mordenite base. An isomerizanum or palladium metal, as contrasted to non-homotion reactor was charged with a appropriate amount of geneous dispersion, has a markedeffect on isomerizathe catalyst, prepared according to the process of Extion selectivity, both in production of desired disubstiample l, and was reduced by heating in hydrogen for a tuted isomers and in reduction of cracking. period of 2 hours at a temperature of 700F. At the end The noble metal deposited on the catalyst surface of this time the isomerization reaction was carried out must be reduced to the metallic state to achieve cataby feeding n-pentane through the reactor at a liquid lytic activity. This is conveniently accomplished by hourly space velocity (LHSV) of 0.625.The isomerizacontact with hydrogen at elevated temperatures. It has tion was carried out at a hydrogen pressure of 450 been found that when the reduction temperature exp.s.i.g. and hydrogen to oil molar ratio of 6. Comparaceeds about 930F the dispersion of metal is impaired. tive runs were made in which the selectivity for forma- The metal tends to agglomerate even in the presence of tion of isopentane and the percent hydrocracking were the cerium and loss of active metal surface and catacompared with a catalyst containing 0.6% platinum on lytic activity results. This loss is minimized by control hydrogen mordenite, our catalyst containing both 0.5% of the reduction temperature at 500 to 900F and pref- Pd and 1% ceria and 0.5 Pd and 0.5% ceria also on hyerably about 700F. drogen type mordenite base. The data collected is set The feed to the isomerization process using the cataout in Table l.

i TABLE I 0.6% Pt on 0.5% Pd 1% ceo 0.5% Pd 0.5% Ceo Catalyst H*- Mordenite on H"- Mordenite on H+ Mordenite Temp., F 550 550 550 W137: Conv. 71 70.8 69.9 i-C Selectivity 82.5 95.4 93.0 7k Hydrocracking 10.2 g 2.1 3 4.8

lyst of the present invention can be substantially pure It is apparent from a review of these data that there is normal paraffms having 4 to 7 carbon atoms, mixture a substantial improvement in the isopentane selectivity and a substantial decrease in hydrocracking when using our catalyst containing as little as 0.5% ceria. Increasing the ceria to 1% results in a slight improvement in isopentane selectivity and a decrease in the percent hydrocracking.

EXAMPLE 3 This example compares the results obtained with a 0.6% platinum on acid-leached mordenite with a catalyst containing 0.5% palladium and 1% ceria on acidleached mordenite. The isomerization was carried out using the same technique as described in Example 1. The acid-leached mordenite was prepared using the general technique described previously. The data collected in these runs is set out in the table below.

Table I] 0.6% Pt on acid- 0.5% Pd 1% CeO Catalyst leached Mordenite on acid-leached Mordenite Temp.. F 550 550 Wt. 7c Conv. 7L2 70 7: if -Selectivity 81.6 93.9

Table lI-continued 0.6% Pt on acid- 0.5% Pd 1% ceo.,

Catalyst leached Mordenite on acid-leached Mordenite Hydrocracking l0 .0 3 .8

it is apparent from review of these data that substantial 1m rovement is isopentane select vity is achieved when e base is acid-leached mordenite The percent hydrocracking is also decreased substantially.

What is claimed is:

l. A process for h droisomerization of paraffins, having from 4 to 7 car It atoms per molecule, at a temperature of 400 to 650F., a pressure of 30 to 500 psig. and a h drogen to hydrocarbon mole ratio of 3 to to 10 to l, y contacting said araffins with a catalyst 

1. A PROCESS FOR HYDROISMERIZATION OF P RAFFINS, HAVING FROM 4 TO 7 CARBON ATOMS PER MOLECULE, AT A TEMPERATURE OF 400* TO 653*F., A PRESSURE OF 300 TO 500 PSIG. AND A HYDROGEN TO HYDROCARBON MOLE RATIO OF 3, TO 10 TO 1, BY CONTACTING SAID PARAFFINS WITH A CATALYST COMPRISING FROM ABOUT 0.1 TO 1.5 WEIGHT PERCENT OF A METAL SELECTED FROM THE GROUP CONSISTING OF PLATINUM AND PALLADIUM AND FROM ABOUT 0.1 TO 5 WEIGHT PERCENT CERIUM OXIDE, SAID PLATINUM OR PALLADIUM HOMOGENOUSLY DISPERSED AS CRYSTALLITES IN THE 5 TO 30 ANGSTROM SIZE RANGE, THE METAL BEING DISPERSED INTO HYDROGEN FORM MODERNITE BY CONTACTING THE BASE WITH A MIXED SOLUTION OF PLATINUM OR PALLADIUM NITRATE AND CERIUM NITRATE FOLLOWED BY CONTROLLED CALCINATION AND REDUCTION WITH HYDROGEN AT A TEMPERATURE OF 500* TO 900*F. 